Javascript Promise Function Style -
suppose have function return promise based on input value need calculated first. seems there 2 ways this.
example 1:
function foo(val) { var newval = val + 100; var anotherval = newval % 12; var returnval = anotherval * 3; return new promise(function(resolve, reject) { settimeout(function() { resolve(returnval); }, 1000); }); } foo(10).then(function(val) { console.log(val); });example 2:
function foo(val) { return new promise(function(resolve, reject) { var newval = val + 100; var anotherval = newval % 12; var returnval = anotherval * 3; settimeout(function() { resolve(returnval); }, 1000); }); } foo(10).then(function(val) { console.log(val); });the first example keeps of setup outside of promise function. , second moves of logic inside of function. on surface these seem equivalent in pretty every scenario. wondering if had insight whether 1 of these better other? or if missing method better these two?
thanks!
the difference between 2 functions variables initialised, difference being variable scope. 2 functions both return same result promise, first approach has benefit of being able access variables within function, while outside of promise.
variables outside promise:
function foo(val) { var newval = val + 100; var anotherval = newval % 12; var returnval = anotherval * 3; console.log(returnval); // returns 6 return new promise(function(resolve, reject) { settimeout(function() { resolve(returnval); }, 1000); }); } foo(10).then(function(val) { console.log(val); });variables inside promise:
function foo(val) { console.log(returnval); // variable doesn't exist return new promise(function(resolve, reject) { var newval = val + 100; var anotherval = newval % 12; var returnval = anotherval * 3; settimeout(function() { resolve(returnval); }, 1000); }); } foo(10).then(function(val) { console.log(val); });as such, depends on how want use variables. if you'd utilise them outside of promise, opt first of 2 functions. if know you're never going need access variables outside of promise, define them within promise prevent variable scope leaking, in turn improving memory.
hope helps! :)
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